Portable VS Black Tanks
 

Ok, so yet another posting. Suppose I could have just added this under my build thread, but in case anyone stopped reading it, I wanted as many answers as possible.

So we all know what happens if you dont vent you black water tanks. Gases build, and the tanks go BOOOOM. usually covering the bathroom with a new 'paint job'. :(

So why do portable toilets not require vents? Is the 4-5 gallon capacity not sufficent to create a problem? This is something that has been on my mind for some time. I bought a portable few months back to use in 'emergencies' (I have used it a total of 2 times since I bought it..but it still beats the 5 gallon bucket) and I dont see it getting huge usage, but I wondered about the gas buildup.

the main reason for venting the tanks is to allow air to flow in to the tank when you are dumping the tank into the waste station, this prevents a vacuum and allows the wast to flow freely down the drain. Same reason plumbing fixtures in your house are vented. The little portable toilets do not have the volume to need a vent to dump/pour out.